<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style type="text/css">
		*{
			margin:0;
			padding:0;
		}
		#demo{
			width: 400px;
			height: 200px;
			background: #ccc;
			margin:200px auto;
			position: relative;
			overflow: hidden;
		}
		.first,.second{
			width: 100px;
			height: 100px;
			position: absolute;
			background:#fc0;
			border-radius: 50px;
		}
		.first{
			top:-50px;
			left:-50px;
		}
		.second{
			bottom:-50px;
			right: -50px;
		}
	</style>
</head>
<body>
	<div id="demo">
		<div class="first"></div>
		<div class="second"></div>
	</div>
</body>
</html>